This invention relates to a screw-type clamp suitable for gripping structural members such as metal plates, beams, angles and the like in order, for example, to lift such members and to hold them in place for assembly into a structure.
The prior art contains numerous types of clamps suitable for gripping metal plates and the like. The majority of these prior art clamps incorporate one generally fixed jaw and another movable jaw which is somehow brought into contact with the material to be lifted. Some of the prior art devices, known as screw clamps, have incorporated a threaded shaft for advancing one jaw into engagement with the member to be clamped. Examples of such devices are disclosed in U.S. Pat. No. 4,183,571 and certain prior art identified therein. When a structural member is lifted by a screw clamp, the member may swing about and be twisted within the slot in which it is secured, thereby applying a torque to the screw shaft. Care must be exercised to maintain a secure grip during such twisting. While the device shown in U.S. Pat. No. 4,183,571 represents a substantial improvement in providing secure gripping action, the present invention adds another dimension resulting in further improvement for certain applications.
To alleviate some of the problems, some prior art clamps have used a ball and socket type of joint connecting the fixed jaw to the clamp body. These prior art devices have suffered significant disadvantages in operation. They have not alleviated the adverse effects of the torque that is applied to the opposing jaw. Prior art ball and socket type joints are also difficult to assemble and replace.